Process control systems often employ fluid control valves to control a flow of fluid. In some low-flow sanitary fluid valves, a valve stem moves within a bonnet that houses a roller assembly. In operation, an actuator moves the valve stem through the bonnet, which causes the roller assembly to move a plate attached to a piston that moves a fluid control member (e.g., a membrane or diaphragm) relative to an orifice or valve seat to control fluid flow.
In such low-flow applications, the movements of the piston are relatively small and, thus, such valves must be calibrated accurately to tightly control the relationship between the movement of the valve stem and the movement of the piston. In many such known valves, this calibration is performed at the time of manufacture (e.g., in a factory setting) by holding the valve stem, the plate and the piston at fixed positions relative to the bonnet (e.g., such that the valve is in a closed position) and then affixing the piston to the plate (e.g., gluing with adhesive). As a result, any recalibration to these known valves typically requires disassembly and/or rebuilding of the valves (e.g., in a manufacturing environment).